During charging of or discharging of a rechargeable battery, gas may occur in a container for a cell included in the rechargeable battery depending on conditions for use of the rechargeable battery and thus cause pressure to increase in the container. When pressure in the container reaches pressure that causes activation of a safety valve provided for the container, the safety valve is activated which in turn releases the gas from the container to the outside. As a result, bursting of the container for the cell can be prevented. However, since the gas released by the operation of the safety valve is combustible electrolyte vapor, the gas may affect human health and may ignite. Therefore, stopping charging of or discharging of the rechargeable battery before activation of the safety valve is desirable.
A battery pack disclosed in Patent Literature 1 includes cells and determines whether there occurs dilatation of the cells by detecting contact between conductors placed on main walls of cell casings for the cells. An electric vehicle control device disclosed in Patent Literature 2 measures internal pressure of a secondary battery with a sensor, and in a case where the internal pressure is greater than a threshold pressure, the electric vehicle control device displays information about occurrence of malfunction of the battery, forbids the secondary battery from being charged, and stops an engine. A battery charge controlling device disclosed in Patent Literature 3 detects a pressure increase in a container based on a signal outputted from a strain sensor that is provided for the container that houses cells.